Add UMA to estimate deroppable memory usage of encoded data size in Resources

third_party/WebKit/Source/core/style/StyleFetchedImage.h

Index: third_party/WebKit/Source/core/style/StyleFetchedImage.h
diff --git a/third_party/WebKit/Source/core/style/StyleFetchedImage.h b/third_party/WebKit/Source/core/style/StyleFetchedImage.h
index 70d9cd9e2616f5793ab01eaf173e507f2b6fcada..b261caf307035dc97bf15cabc9574adadd711e2d 100644
--- a/third_party/WebKit/Source/core/style/StyleFetchedImage.h
+++ b/third_party/WebKit/Source/core/style/StyleFetchedImage.h
@@ -68,6 +68,12 @@ class StyleFetchedImage final : public StyleImage, private ResourceClient {
   bool knownToBeOpaque(const LayoutObject&) const override;
   ImageResource* cachedImage() const override;
 
+  bool isRefetchableFromDiskCache() const override {
+    // ResourceFetcher is not determined from StyleFetchedImage and it is
+    // impossible to send a request for refetching.
+    return false;
+  }
+
   DECLARE_VIRTUAL_TRACE();
 
  private: